The invention relates to a device for capacitive reading of data carriers, such as labels, which comprise a substrate of non-conductive material which carries at predetermined marking locations special markings in conductive material which can be formed for example by printing on conductive ink or applying metal foil. Such devices are known from No. DE-C-28 17 388.
The electronic data techniques which are establishing themselves in all areas of industry require new methods and means for automatic identification of articles. The optically readable bar code labels as used in department stores are an example. In production lines automatically readable codes are required to enable the material flow to be controlled. For identification of railway carriages a system exists operating with resonance circuits in the microwave range. If it is required to detect whether an article is genuine machine-readable labels are required whose information must be difficult to interpret without such aids and proof against forgery. For identifying articles exposed to rough ambient conditions the label must be very robust. For mass-produced articles particular demands are made of the simple and economic production of the labels.
The known labels and the associated readers or scanners inadequately meet or completely fail to meet the requirements as regards robustness, proof against forgery and economic production.
Admittedly, in the case of bar code scanners the labels are cheap to make but the information is visible and can therefore be falsified; moreover, soiling leads to reading errors. Other reading devices, such as microwave resonance circuits, are too complicated. The latter also applies to data carriers consisting of variable permanent magnets.